sd-login: sd_get_machine_names(): do not return -EINVAL when output parameter is NULL

Other functions in sd-login generally allow the output parameter to be NULL, in
which case only the number of items that would be stored in the array is returned.
Be nice and do the same here.

2 files changed, 8 insertions, 7 deletions

diff --git a/src/libelogind/sd-login/sd-login.c b/src/libelogind/sd-login/sd-login.c
index 7630e6265..5f90ba70c 100644
--- a/src/libelogind/sd-login/sd-login.c
+++ b/src/libelogind/sd-login/sd-login.c
@@ -942,14 +942,13 @@ _public_ int sd_get_uids(uid_t **users) {
 }
 
 _public_ int sd_get_machine_names(char ***machines) {
-        char **l = NULL, **a, **b;
+        char **l, **a, **b;
         int r;
 
-        assert_return(machines, -EINVAL);
-
         r = get_files_in_directory("/run/systemd/machines/", &l);
         if (r == -ENOENT) {
-                *machines = NULL;
+                if (machines)
+                        *machines = NULL;
                 return 0;
         }
         if (r < 0)
@@ -959,7 +958,7 @@ _public_ int sd_get_machine_names(char ***machines) {
                 r = 0;
 
                 /* Filter out the unit: symlinks */
-                for (a = l, b = l; *a; a++) {
+                for (a = b = l; *a; a++) {
                         if (startswith(*a, "unit:") || !machine_name_is_valid(*a))
                                 free(*a);
                         else {
@@ -972,7 +971,8 @@ _public_ int sd_get_machine_names(char ***machines) {
                 *b = NULL;
         }
 
-        *machines = l;
+        if (machines)
+                *machines = l;
         return r;
 }
 
diff --git a/src/libelogind/sd-login/test-login.c b/src/libelogind/sd-login/test-login.c
index 3dc797530..3eb11cf4a 100644
--- a/src/libelogind/sd-login/test-login.c
+++ b/src/libelogind/sd-login/test-login.c
@@ -251,8 +251,9 @@ static void test_login(void) {
                 assert_se(r >= 0);
                 assert_se(r == (int) strv_length(machines));
                 assert_se(buf = strv_join(machines, " "));
-
                 log_info("sd_get_machines(…) → [%i] \"%s\"", r, buf);
+
+                assert_se(sd_get_machine_names(NULL) == r);
         }
 }